1. Field of the Invention
The present invention relates to a method for operating a hybrid vehicle including an internal combustion engine and an electric machine.
2. Description of the Related Art
Hybrid vehicles usually include an internal combustion engine as a main drive and at least one auxiliary drive. One such auxiliary drive is in particular designed as an electric machine. A drive torque for driving the hybrid vehicle is generated by the internal combustion engine. This drive torque is transmitted, among others, via the transmission and the drive shaft to the wheels of the hybrid vehicle, a wheel drive torque each being generated by the internal combustion engine at the wheels of the hybrid vehicle.
With the aid of the electric machine, a boost recuperation system (BRS), for example, may be implemented. For this purpose, the electric machine may be connected via a belt, for example, to the crankshaft of the internal combustion engine.
In a generator operating mode, the electric machine absorbs a drive torque and converts mechanical energy into electrical energy. The wheel drive torque at the wheels is reduced during this process by the electric machine. The electric machine thus generates a “negative” active wheel drive torque.
In a motor operating mode, the electric machine converts electrical energy back into mechanical energy and generates a drive torque. The wheel drive torque at the wheels is increased during this process by the electric machine. The electric machine thus generates a “positive” active wheel drive torque.
A total wheel drive torque at the wheels is thus composed of the wheel drive torque of the internal combustion engine and of the wheel drive torque of the electric machine.
Driver assistance functions are safety measures which may act in a wheel drive torque-increasing or wheel drive torque-reducing way. In unstable or stability-critical driving states, such driver assistance functions may intervene in the vehicle dynamics in a stabilizing manner. Such safety measures may influence in particular the internal combustion engine or the brakes in order to either increase or reduce the wheel drive torque and to thus stabilize the vehicle dynamics. Such safety measures are, for example, the electronic stability program (ESP), the engine drag torque control (MSR), the traction control system (TCS) or the anti-lock braking system (ABS).
However, in hybrid vehicles there is the risk of such unstable or stability-critical driving states becoming increasingly worse due to the wheel drive torque of the electric machine despite the safety measure attempting to stabilize the vehicle dynamics. An accident risk may thus be increased and there is a considerable danger for occupants of the hybrid vehicle as well as other road users.
Although the electric machine may be shut off in such situations, unstable or stability-critical driving states may in certain cases become even worse due to this shut-off of the electric machine and the thus sudden loss of wheel drive torque of the electric machine. The accident risk may thus be even increased by the uncontrolled shut-off of the electric machine during unstable or stability-critical driving states.
It is therefore desirable to provide a possibility of stabilizing a hybrid vehicle in unstable or stability-critical driving states in a safe manner.